有序数组转换为平衡二叉树(BST)

把有序数组转换为平衡二叉树。

<pre name="code" class="cpp">TreeNode* buildTree(vector<int> &nums,int start,int last){int mid = (start + last) / 2;TreeNode *root = new TreeNode(nums[mid]);if(start == last){return root;}if(start <= mid - 1){root->left = buildTree(nums,start,mid-1);}if(mid+1 <=  last){root->right = buildTree(nums,mid+1,last);}return root;}TreeNode* sortedArrayToBST(vector<int>& nums) {if(nums.empty())return NULL;return buildTree(nums,0,nums.size()-1);}